I have a house bank of lead -acid golf cart batteries consisting of 4 225 ah 6 v Costco batteries wired in parallel and series to get me 12 vdc; I also need a source for 24 vdc requiring 2 amps intermittently; can I wire something to my present house battery to also gather 24 vdc and still provide the basic house function of 12 vdc or should I look at DC2DC converters?

Impracticle yes, but not entirely impossible. It can be done by wiring all 4 batteries in series, and taking a tap off the top battery + for 24V, and off the 2nd battery + for 12V. There are some limitations/considerations.

1) The batteries on the "bottom" providing the 0-6V and 6-12V sections will be working doubly hard, since they are supplying both the 12V and 24V rails. They will likely discharge very fast and bring both your 12V and 24V rails down sooner than in your current configuration.
2) Your 12V supply power capacity will be halved since you only have 2 batteries supplying 12V instead of your previous 4.
3) Charging will be a concern. Youd have to charge at the 24V level at the top of your series chain. I dont think you will be able to charge the bottom 2 batteries on a 12V charge line alone.

If i were you i'd get a single 24V battery with a small dedicated charger for your intermittent 2A load. Maybe a single dedicated solar panel designed for 24V that is connected all the time.

Question... what is the daily power consumption of this 2A load? Can you express it in "hours on per day"?

Don't mess with tricky wiring of your batteries. So very many things can go wrong that it hardly justifies the slight gain in efficiency for that one 24v consumer . . . It's hard enough to balance the charging and loads on a multi-battery bank as it is without such shenanigans . . .

Unless we're talking about a big consumer like a windlass or a bowthruster, which really cry out for 24v . . .

Better yet, in any case, just convert the whole boat to 24v. It's better

I have 24vdc on my power boat. I also have a huge, old 12vdc house bank that I will replace this spring with 4 each 6vdc batteries. I also have a separate battery for my generator.

Back to the 24 volt bank......... its purpose is two fold. First I dread the thought of having my Maxwell HWC2200 windlass run a battery down when the windlass must be functional. Also because the windlass has a large current draw I wanted to avoid the voltage drop in the wiring to the windlass.

I also use the 24vdc bank to operate a 1500 watt inverter that provides power to our TV, laptop & microwave. We can watch TV all day & night without noticeably discharging that bank. As a point of interest, the higher your DC supply voltage is, the higher your conversion efficiency will be.

The house bank is used for starting AND to power a 1KW true sinewave inverter for our 8.3cu ft fridge that has an interior light AND IS SELF DEFROST.

My humble opinion is that boats, cars and trucks should be using much higher voltages because of the increase in efficiencies at higher voltages.

Better yet, in any case, just convert the whole boat to 24v. It's better

Good suggestion if one was just starting to build a boat. To change everything on an existing boat is a big step that will impact too many things. But I do agree that 24 OR higher voltages have advantages.

The bass fishing boats do this all the time to run their 24 volt trolling motors and charge their 24 volt battery from the 12 volt alternator using one extra battery. When the extra battery is not being used for the 24 volt load it is automatically put in parallel with the main 12 volt battery. Check Trollbridge24 on Google.